Inbred corn line LH218

ABSTRACT

An inbred corn line, designated LH218, is disclosed. The invention relates to the seeds of inbred corn line LH218, to the plants of inbred corn line LH218 and to methods for producing a corn plant produced by crossing the inbred line LH218 with itself or another corn line. The invention further relates to hybrid corn seeds and plants produced by crossing the inbred line LH218 with another corn line.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinctive corn inbred line, designated LH218. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include higher yield, resistance to diseases and insects, better stalks and roots, tolerance to drought and heat, and better agronomic quality.

Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F₁ hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.

The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.

Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).

Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.

These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.

A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.

The goal of plant breeding is to develop new, unique and superior corn inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same corn traits.

Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The inbred lines which are developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new corn inbred line.

The development of commercial corn hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential.

Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents which possess favorable, complementary traits are crossed to produce an F₁. An F₂ population is produced by selfing one or several F₁ 's or by intercrossing two F₁ 's (sib mating). Selection of the best individuals is usually begun in the F₂ population; then, beginning in the F₃, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F₄ generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F₆ and F₇), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.

Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.

Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.

Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Allard, 1960; Simmonds, 1979; Sheep et al., 1979; Fehr, 1987).

Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.

Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced when two inbred lines are crossed to produce the F₁ progeny. A double-cross hybrid is produced from four inbred lines crossed in pairs (A×B and C×D) and then the two F₁ hybrids are crossed again (A×B)×(C×D). Much of the hybrid vigor exhibited by F₁ hybrids is lost in the next generation (F₂). Consequently, seed from hybrid varieties is not used for planting stock.

Corn is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding corn hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of grain produced on the land used and to supply food for both animals and humans. To accomplish this goal, the corn breeder must select and develop corn plants that have the traits that result in superior parental lines for producing hybrids.

SUMMARY OF THE INVENTION

According to the invention, there is provided a novel inbred corn line, designated LH218. This invention thus relates to the seeds of inbred corn line LH218, to the plants of inbred corn line LH218 and to methods for producing a corn plant produced by crossing the inbred line LH218 with itself or another corn line. This invention further relates to hybrid corn seeds and plants produced by crossing the inbred line LH218 with another corn line.

DEFINITIONS

In the description and tables which follow, a number of terms are used. In order to provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided:

Predicted RM

This trait for a hybrid, predicted relative maturity (RM), is based on the harvest moisture of the grain. The relative maturity rating is based on a known set of checks and utilizes conventional maturity systems such as the Minnesota Relative Maturity Rating System.

MN RM

This represents the Minnesota Relative Maturity Rating (MN RM) for the hybrid and is based on the harvest moisture of the grain relative to a standard set of checks of previously determined MN RM rating. Regression analysis is used to compute this rating.

Yield (Bushels/Acre)

The yield in bushels/acre is the actual yield of the grain at harvest adjusted to 15.5% moisture.

Moisture

The moisture is the actual percentage moisture of the grain at harvest.

GDU Silk

The GDU silk (=heat unit silk) is the number of growing degree units (GDU) or heat units required for an inbred line or hybrid to reach silk emergence from the time of planting. Growing degree units are calculated by the Barger Method, where the heat units for a 24-hour period are: ##EQU1## The highest maximum used is 86° F. and the lowest minimum used is 50 ° F. For each hybrid, it takes a certain number of GDUs to reach various stages of plant development. GDUs are a way of measuring plant maturity.

Stalk Lodging

This is the percentage of plants that stalk lodge, i.e., stalk breakage, as measured by either natural lodging or pushing the stalks determining the percentage of plants that break off below the ear. This is a relative rating of a hybrid to other hybrids for standability.

Root Lodging

The root lodging is the percentage of plants that root lodge; i.e., those that lean from the vertical axis at an approximate 30° angle or greater would be counted as root lodged.

Plant Height

This is a measure of the height of the hybrid from the ground to the tip of the tassel, and is measured in centimeters.

Ear Height

The ear height is a measure from the ground to the ear node attachment, and is measured in centimeters.

Dropped Ears

This is a measure of the number of dropped ears per plot, and represents the percentage of plants that dropped an ear prior to harvest.

DETAILED DESCRIPTION OF THE INVENTION

Inbred corn line LH218 is a yellow dent corn with superior characteristics, and provides an excellent parental line in crosses for producing first generation (F₁) hybrid corn,

LH218 is a line developed from the hybrid LH51×LH123, where F₁ plants were selfed two times. These LH51×LH123)S₂ plants were then crossed to LH50. The [LH51×LH123)S₂ ×LH50] cross was then selfed four generations to produce LH218. LH218 was first observed as having unique and extraordinary traits in 1991. 1991 was an atypical year for hybrid grain dry down and general plant deterioration. While the hybrids in the same tests as LH218 hybrids were losing their tops and generally "melting down" or showing plant deterioration, the LH218 hybrids still exhibited excellent plant intactness. The differences in plant intactness were most evident between LH218 and other related lines of the same genetic background.

Some of the criteria used to select ears in various generations include: yield, stalk quality, root quality, disease tolerance, late plant greenness, late season plant intactness, ear retention, pollen shedding ability, silking ability, and corn borer tolerance. During the development of the line, crosses were made to inbred testers for the purpose of estimating the line's general and specific combining ability, and evaluations were run by the Franklin, Indiana Research Station. The inbred was evaluated further as a line and in numerous crosses by the Franklin and other research stations across the Corn Belt. The inbred has proven to have a very good combining ability in hybrid combinations.

The inbred has shown uniformity and stability for all traits, as described in the following variety description information. It has been self-pollinated and ear-rowed a sufficient number of generations, with careful attention to uniformity of plant type to ensure homozygosity and phenotypic stability. The line has been increased both by hand and sibbed in isolated fields with continued observation for uniformity. No variant traits have been observed or are expected in LH218. Inbred corn line LH218 has the following morphologic and other characteristics (based primarily on data collected at Williamsburg, Iowa):

VARIETY DESCRIPTION INFORMATION

A. Maturity

INBRED=LH218

Best Adapted For: Southeast Regions of the Corn Belt

Heat Unit Silk: 1465 ##EQU2##

B. Plant Characteristics

Plant height (to tassel tip): 237 cm.

Length of top ear internode: 16 cm.

Number of tillers: None

Cytoplasm type: Normal

Number of ears per stalk: Single

Ear height (to base of top ear): 93 cm.

C. Leaf

Color: 5 GY 4/4 Munsell Color Charts for Plant Tissues

Angle from stalk: 30°-60°

Marginal waves: few

Width (widest point of ear node leaf): 10 cm.

Number of leaves (mature plants): 12

Sheath pubescence: Light

Longitudinal creases: Few

Length (ear node leaf): 74 cm.

D. Tassel

Number of lateral branches: 6

Branch angle from central spike: <30°

Pollen shed: Heavy

Anther color: Yellow

Glume color: Green with brown margin

Peduncle length (top leaf to basal branch): 16 cm.

E. Ear (Husked Ear Data Except When Stated Otherwise)

Length: 17 cm.

Midpoint diameter: 41 mm.

Weight: 108 gm.

Number of Kernel rows: 10

Silk color: Green

Husk color (fresh): Light green

Husk color (dry): Buff

Husk extension: Very long (>10 cm.)

Shank length: 14 cm.

Shank (no. of internodes): 8

Taper of Ear: Average

Husk leaf: <8 cm.

Position of shank (dry husks): Upright

F. Kernel (Dried)

Size (from ear midpoint)

Length: 11 mm.

Width: 10 mm.

Thickness: 4 mm.

Shape grade (% rounds): 40-60

Pericarp color: Variegated: bronze at the pedicel becoming colorless at the crown

Aleurone color: White

Endosperm color: Yellow

Endosperm type: Normal starch

Gm Weight/100 seeds (unsized): 34 gm.

G. Cob

Diameter at midpoint: 30 mm.

Strength: Strong

Color: Red

This invention is also directed to methods for producing a corn plant by crossing a first parent corn plant with a second parent corn plant, wherein the first or second corn plant is the inbred corn plant from the line LH218. Further, both first and second parent corn plants may be from the inbred line LH218. Therefore, any methods using the inbred corn line LH218 are part of this invention: selfing, backcrosses, hybrid breeding, and crosses to populations. Any plants produced using inbred corn line LH218 as a parent are within the scope of this invention. Advantageously, the inbred corn line is used in crosses with other corn varieties to produce first generation (F₁) corn hybrid seed and plants with superior characteristics.

As used herein, the term "plant" includes plant cells, plant protoplasts, plant cell of tissue culture from which corn plants can be regenerated, plant calli, plant clumps, and plant cells that are intact in plants or parts of plants, such as pollen, flowers, kernels, ears, cobs, leaves, husks, stalks, and the like.

Tissue culture of corn is described in European Patent Application, Publication No. 160,390, incorporated herein by reference. Corn tissue culture procedures are also described in Green and Rhodes, "Plant Regeneration in Tissue Culture of Maize", Maize for Biological Research (Plant Molecular Biology Association, Charlottesville, Va. 1982), at 367-372. Thus, another aspect of this invention is to provide for cells which upon growth and differentiation produce the inbred line LH218.

The closest related art to LH218 is not clear; it does not resemble any one line more than another. LH50 is not being used to any extent at the present time, nor is LH123. LH51 was chosen for comparison because it makes up theoretically one-quarter of the parentage and it is a widely used commercial line. LH213 was chosen for comparison because one-half of the parentage of LH218 is the same population from which LH213 was developed.

Table 1 shows the interpretation of disease ratings and Table 2 shows head to head comparisons of LH218 versus LH51 in hybrid combinations. Column 2 of Table 1 indicates the pedigrees tested and column 4 shows the total number of geographical locations where these pedigrees were compared. Column 5 (#1 Hybrid Mean) shows the mean values of the first genotype listed in column 2. Column 6 indicates the trait or characteristics (Yield, Moisture, Stalk Lodging and Root Lodging). Column 7 shows the difference between the first genotype listed in column 2 versus the second genotype (Genotype #1 minus Genotype #2). Column 8 shows the statistical probability and column 9 indicates general notes on the comparison.

                  TABLE 1                                                          ______________________________________                                         INTERPRETATION OF DISEASE RATINGS                                              Rating                                                                         ______________________________________                                         0 =      0% of the plant showing lesions                                       1 =      Less than 5% of the plant covered with lesions                        2 =      Less than 10% of the plant covered with lesions                       3 =      Less than 30% of the plant covered with lesions                       4 =      Less than 40% of the plant covered with lesions                       5 =      Less than 50% of the plant covered with lesions                       6 =      Less than 60% of the plant covered with lesions                       7 =      Less than 70% of the plant covered with lesions                       8 =      Less than 80% of the plant covered with lesions                       9 =      80-100% of the plant covered with lesions                             ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________     LH218 - Head to Head Comparisons                                               Comparison                                                                            Pedigrees      #1 Hybrid                                                No.    Compared Year                                                                              Loc.                                                                              Mean  Trait                                                                              Diff.                                                                               Prob.                                                                              Notes                                 __________________________________________________________________________     1      LH195 × LH218                                                                     1992                                                                              85 197.00                                                                               Yield                                                                              -4.588                                                                              .017                                             LH195 × LH51                                                                         85 21.33 Mst +0.200                                                                              .168                                                         80 1.75  Stalk                                                                              -0.175                                                                              .621                                                         72 2.99  Root                                                                               -1.958                                                                              .018                                      2      LH132 × LH218                                                                     1992                                                                              31 202.65                                                                               Yield                                                                              -0.419                                                                              .910                                             LH132 × LH51                                                                         31 21.68 Mst -0.641                                                                              .001                                                         31 1.52  Stalk                                                                              -2.484                                                                              .069                                                         30 6.43  Root                                                                               -3.567                                                                              .045                                      3      LH192 × LH218                                                                     1992                                                                              26 211.92                                                                               Yield                                                                              +7.038                                                                              .022                                             LH132 × LH51                                                                         26 24.16 Mst +1.087                                                                              .001                                                         26 1.35  Stalk                                                                              -1.000                                                                              .112                                                         23 6.130 Root                                                                               -5.783                                                                              .057                                      4      LH192 × LH218                                                                     1992                                                                              26 211.92                                                                               Yield                                                                              +3.231                                                                              .239                                             LH192 × LH213                                                                        26 24.16 Mst -1.367                                                                              .000                                                         26 1.35  Stalk                                                                              +0.462                                                                              .232                                                         23 6.130 Root                                                                               -3.783                                                                              .094                                      5      LH195 × LH218                                                                     1991                                                                              14 154.14                                                                               Yield                                                                              +8.500                                                                              .032                                             LH195 × LH51                                                                         14 17.94 Mst +0.737                                                                              .028                                                         14 1.71  Stalk                                                                              +0.714                                                                              .315                                                         14 0.29  Root                                                                               -2.288                                                                              .289                                      6      LH195 × LH218                                                                     1991                                                                              14 154.14                                                                               Yield                                                                              +5.500                                                                              .191                                             LH195 × LH213                                                                        14 17.94 Mst +0.925                                                                              .004                                                         14 1.710 Stalk                                                                              +0.143                                                                              .851                                                         14 0.29  Root                                                                               -0.429                                                                              .416                                      7      LH192 × LH218                                                                     1991                                                                              16 166.38                                                                               Yield                                                                              +9.375                                                                              .005                                             LH195 × LH51                                                                         16 16.35 Mst -0.048                                                                              .822                                                         16 2.63  Stalk                                                                              -0.500                                                                              .406                                                         15 0.670 Root                                                                               -3.800                                                                              .243                                      8      LH195 × LH218                                                                     1991                                                                              14 154.14                                                                               Yield                                                                              +16.714                                                                             .001                                             LH132 × LH51                                                                         14 17.94 Mst + 1.109                                                                             .001                                                         14 1.71  Stalk                                                                              -1.643                                                                              .069                                                         14 0.29  Root                                                                               -1.071                                                                              .302                                      __________________________________________________________________________

In 1991, LH218 had more yield than LH51 (comparison 5) in 14 locations. This was accompanied by slightly higher moisture and much improved root strength (2% less root lodging which wasn't statistically different, but statistical significance wouldn't be expected given the small number of plots that had any root lodging of the 14 plots in this comparison). In 1992 (comparison 1), this same comparison showed that the LH218 had slightly less yield than LH51, but equal moisture and improved root strength (with more locations this improvement in root strength was highly significant). The significantly higher yield in 1991, and the significantly lower yield in 1992, show that LH218 performs more favorably in environments which occurred in 1991, rather than the cool, slow drying year of 1992. Comparison 2 also compares LH218 and LH51 in a cross with LH132 in 1992. Comparison 2 shows the LH218 to be equal in yield, significantly lower moisture, and better for stalks (p=0.069) and with less root lodging.

In 1991 LH218 showed a tendency to yield more than LH213 when crossed with LH195 (comparison 6), but this was accompanied by higher moisture. LH213 and LH218 are similar in the trait of late season intactness. There was a tendency for the LH218 hybrid to have less root lodging. LH218 was compared to LH213 with analogous crosses using LH192 in 1992 (comparison 4). Again there is a tendency for higher yield with the LH218, accompanied this time by significantly lower moisture, and a strong tendency for less root lodging. This wide difference in moistures between LH218 crosses and the LH213 crosses in two different years demonstrates diverse reaction to different environmental conditions between these two lines.

In comparisons 3, 7, and 8, LH218 crosses are compared with the widely grown hybrids LH132×LH51 (comparisons 3 and 8) and LH195×LH51 (comparison 7). In all three of these comparisons the LH218 hybrid showed that it had improved standability for both stalk and root (the probabilities vary but the consistency of this improvement strongly suggests that it is valid). In all three of these comparisons the LH218 hybrid had significantly higher yield. The LH218 hybrids offer high yielding, excellent standing hybrids, that are diverse from current widely grown hybrids.

DEPOSIT INFORMATION

Inbred seeds of LH218 have been placed on deposit with the American Type Culture Collection (ATCC), Rockville, Md. 20852, under Deposit Accession Number 75566 on Oct. 6, 1993. A Plant Variety Protection Certificate is being applied for with the United States Department of Agriculture.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity and understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the invention, as limited only by the scope of the appended claims. 

What is claimed is:
 1. Inbred corn seed designated LH218 having ATCC accession No.
 75566. 2. A corn plant produced by growing the seed of claim
 1. 3. Pollen of the plant of claim
 2. 4. An ovule of the plant of claim
 2. 5. An inbred corn plant having all the physiological and morphological characteristics of the corn plant of claim
 2. 6. A tissue culture comprising regenerable cells of the inbred corn plant designated LH218, wherein the seeds of LH218 have been deposited as ATCC Accession No.
 75566. 7. A corn plant regenerated from the tissue culture of claim 6, wherein said corn plant has all the physiological and morphological characteristics of LH218, wherein the seeds of LH218 have been deposited as ATCC Accession No.
 75566. 